Pass an object with the options as second parameter to JSLINT. Global variables can be defined as an array of strings and assigned to the predef property of said options object.
From the JSLint source code:
JSLINT is a global function. It takes two parameters.
var myResult = JSLINT(source, option);
The first parameter is either a string or an array of strings. If it is a
  string, it will be split on '\n' or '\r'. If it is an array of strings, it
  is assumed that each string represents one line. The source can be a
  JavaScript text, or HTML text, or a JSON text, or a CSS text.
The second parameter is an optional object of options that control the
  operation of JSLINT. Most of the options are booleans: They are all
  optional and have a default value of false. One of the options, predef,
  can be an array of names, which will be used to declare global variables,
  or an object whose keys are used as global names, with a boolean value
  that determines if they are assignable.